of CO production from tobacco combustion is not well known and may vary considerably as a function of a number of variables (puff volume, puff duration, temperature, etc.). The ratio of CO, a nonreactive contaminant, to the more reactive gas-phase contaminants in ETS and to reactive suspended particulate mass is not well established, particularly in the dynamic phase of smoking, that is, the non-steady-state phase. Chamber and field studies have indicated that, under realistic smoking conditions that would be encountered in residences or offices, the typical smoking and ventilation rates would produce CO levels well within the levels observed in the outdoor air or in the indoor air generated from the indoor sources, such as kerosene heater, gas stove, etc. Consequently, it is difficult to factor out the contribution of CO from ETS in any specific, uncontrolled situation. In areas where heavy smoking is experienced, and where other sources of CO do not exist, CO may provide a rough measure of ETS exposure because the CO produced by the tobacco combustion will dominate.

Both chamber and field studies (Table 5–1) have demonstrated that tobacco combustion has a major impact on the mass of suspended particulate matter in occupied spaces in the size range <2.5 µm, defined in this report as respirable suspended particulates (RSP). Suspended particulate mass is a major component of environmentally emitted tobacco smoke. Even under conditions of low smoking rates, easily measurable increases in RSP have been recorded above background levels (Table 5–1). The term RSP, however, encompasses a broad range of particulates of varying chemical composition and size emanating from a number of sources (outdoors, cooking indoors, etc).

Smoking is not the only source of particulate matter suspended in the indoor air. The apportionment of the measured RSP to tobacco combustion in an occupied space will not be accurate unless the RSP emission rates for a variety of brands of tobacco are similar under a variety of conditions and source use information is obtained. The variability of RSP emissions into the environment for a variety of brands of tobacco needs to be investigated, as does the relationship between the vapor and particulate phases of tobacco-combustion emissions under a variety of environmental conditions, such as different humidities, and under a variety of smoking conditions, such as subject smokers versus smoking machines.